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Errors of Refraction


Total dioptric power of eye is 58 D to 60 D*
Infant is normally hypermetropic upto +3.0 D to + 3.5 D.

Errors of refraction:

  • Myopia                
  • Hypermetropia
  • Astigmatism                 
  • Anisometropia     
  1. Aphakia
    1. Eye becomes highly hypermetropia
    2. Total power of eye is reduced to + 48 D
    3. Loss of accommodation
    4. Best available treatment for aphakia is posterior chamber ( in the bag) intraocular lens.
Other methods of correcting aphakia
  1. Spectacle
  2. Contact lens             
  3. Refractive surgery- Hyperopic LASIK
  1. Anisometropia
    When the total refraction of the two eyes is unequal by > 2 D*
  2. Aniseikonia
    When the images projected to the visual cortex, from the two retinas are abnormally unequal in size and / or shape. Up to 5% of aniseikonia is well tolerated.
  3. Purkinje’s Image
    1. Are of four types
    2. Formed when strong beam of light is projected on eye
    3. 1st and 2nd image by ant and post surface of cornea*
    4. 3rd and 4th image – by anterior and posterior surface of lens*
    5. 4th image- is inverted*
  4. Retinoscopy
    1. Also called skiascopy or shadow test, is an objective method of finding out the error of refraction by the method of neutralization
    2. Observations- Depending upon the movement of red reflex, when a plane mirror retinoscope is used at a distance of 1 metre. The results are interpreted as below
      1. No movement of red reflex indicates myopia of ID*
      2. When red reflex moves along with the movement of the retinoscope, it indicates either emmetropia or hypermetropia or myopia of less than 1 dioptre*
      3. When red reflex moves against the movement of the retinoscope, it indicates myopia of > -1 D*.
The choice of cycloplegic for refraction in < 8 yrs of age is 1% Atropine eye ointment*.

It is applied three times for three days before refraction.

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